This invention relates to a serial printer which prints while moving a carrier provided with a print head.
In this type of serial printer, a print head facing a platen is mounted on a carrier. The serial printer includes a carrier motor composed of a direct-current (DC) motor for driving the carrier and provides acceleration and deceleration control of the carrier motor and moves the carrier along the platen in the direction of main scanning, thereby printing line by line.
Specifically, to print one line, the carrier is accelerated by controlling the carrier motor on the basis of the acceleration data preset so that the carrier may reach a specific constant speed V0 by the time it has arrived at the print start position as shown in FIG. 14. After the carrier motor has reached the constant speed, the print head starts to print. After the printing has been done, the carrier is decelerated by controlling the carrier motor on the basis of the preset deceleration data and is stopped at a specific position. In this way, printing is done line by line repeatedly until one page of print has been completed.
Recently, there have been demands for printers capable of printing at higher speeds. To realize high-speed printing with a serial printer as described above, the constant speed V0, the speed of the carrier in printing, has to be increased.
As the constant speed V0 is made higher, the distance required for acceleration (the acceleration distance) and the distance required for deceleration (the deceleration distance) must be made longer. Because in a serial printer as described above, acceleration control must be completed and constant-speed control be in operation by the time the carrier has reached the print start position. Therefore, the moving range W of the carrier must be made so much longer, leading to the problem of making the printer larger. An attempt to accelerate and decelerate at a stretch in a short distance would cause damping and permit the speed of the carrier to fluctuate as shown in FIG. 15. As a result, the movement of the carrier would be slow in becoming stable and have an adverse effect on the result of printing, leading to, for example, the corruption of the printed image.
Although printing may be done during acceleration or deceleration control of the carrier, variations in the speed of the carrier caused by the occurrence of damping during acceleration or deceleration control can have an adverse effect on the result of printing, leading to, for example, the corruption of the printed image.